Various processes in the fabrication of semiconductor devices require heating of a silicon wafer, or workpiece, to a prescribed temperature. Indeed, there have been continued and ongoing efforts to improve semiconductor manufacturing processes and equipment used therefor that have centered around heating the workpiece. For example, it is well known that high temperature ion implantation, with wafer temperatures in the range of 150-600 C, may offer significant advantages over room-temperature ion implantation. High temperature wafer processing has also been found to assist in the generation and/or enhancement of certain chemical and physical reactions. For example, it may be desirable to raise the temperature of the workpiece to assist in driving off volatile surface impurities. As a further example, it may be desirable to raise wafer temperature following a process in which wafer temperature has been cooled below ambient temperature, so that atmospheric water-vapor present in the vicinity of the wafer does not condense onto the wafer when it is removed from the process tool into the ambient environment.
Heating assemblies for raising the temperature of a semiconductor wafer to an elevated level are well known. For example, U.S. Pat. No. 6,744,017, assigned to IBIS Technology Corp., discloses an ion implantation system typically used in the processing of semiconductor wafers wherein the semiconductor wafer is exposed to a beam of ions having a selected energy and the wafer is heated to elevated temperatures during ion implantation steps. High temperature ion implantation has been found to dynamically anneal defects generated in the wafer as a result of ion bombardment, and/or during subsequent annealing steps.
In another specific example, commonly assigned US Patent Application Publication No. 2011/0291022 describes a problem found in ion implantation processes, wherein a workpiece is typically transferred to a load lock chamber subsequent to implantation of ions. When the load lock chamber is opened to remove the workpiece, condensation can occur that can result in deposition of particles on the workpiece, and/or leave residues on the workpiece. That patent application describes a solution directed toward mitigation of condensation on a workpiece when transferred from a relatively cold environment to a warmer environment by heating the workpiece prior to exposure to the warmer environment. Process heating has previously been accomplished utilizing a number of different methods, including exposing the workpiece to heated vapors, light sources, and/or direct contact thermal-transfer from a heated source. These methods, however, convey energy for heating of the workpiece over a wide range that can be both useful and detrimental to the purpose of increasing the temperature of the workpiece.
In particular, the use of light sources, or more generally, optical heat sources in the processing of silicon wafers is disclosed in U.S. Pat. No. 8,450,193, wherein an exemplary method for heating a wafer for high-temperature ion implantation is described, including an optical heat source that may comprise an array of heater lamps mounted in front of a reflector for emitting light onto the wafer. According to one embodiment, a laser wavelength in the infrared range may be efficiently absorbed by the wafer.
However, heating a silicon wafer via light energy can be problematic because silicon wafers are particularly absorptive of light in the visible range of wavelengths, and transparent to and/or non-absorptive of light in the infrared wavelengths. Since typical incandescent or incandescent-halogen-cycle lamps emit approximately 15-20% of light energy in the visible wavelength, as much as 85% of the light energy is not absorbed by the wafer. In addition to the obvious inefficiencies associated with the use of such optical heat sources, the energy associated with the infrared wavelengths may be detrimentally absorbed by other materials and components in the heating process environment.
Therefore, a need exists in the art for an apparatus, system, and method for efficient optical heating systems for use in processing of silicon wafers, wherein light wavelengths emitted from the optical heating system can be selectively provided within a predetermined range of wavelengths. More specifically, a need exists for an apparatus, system, and method for providing an optical heating source for heating a workpiece, wherein the optical heating source is configured to emit light energy in the visible wavelength range, while emitting reduced light energy in the nonvisible wavelength range.